Curable alkyd resins, often referred to as “air drying” alkyds, are widely used in industry in surface coatings such as paints, in particular decorative paints. They are well known materials, and generally they are film forming polyesters including residues of polybasic, usually di-basic, acid(s) and polyhydroxy, usually tri- or higher hydroxy alcohols and further including monobasic unsaturated (often multiple unsaturated) fatty acid residues. Such alkyd resins may include other residues and/or additives to provide specific functionality for the intended end use, e.g. sources of additional carboxyl groups may be included to improve resin emulsifyability. Curable alkyds are widely included in paints, which may be solvent based, water based or use mixed solvent/water vehicles, in which the alkyd is in the dispersed phase. The alkyds are usually formed into an emulsion before incorporation into the paint and in such emulsions the alkyd is typically dispersed in the water phase as uniformly and generally as finely as is possible, and commonly surfactants, particularly emulsifiers, are used to aid this.
Emulsifiers can contribute to fine and uniform alkyd resin droplets in emulsions. Typical emulsifiers are relatively low molecular weight surfactant materials, which in emulsions tend to be concentrated at or near the resin/water interface. However, during drying of resin films made from emulsions, the emulsifiers tend to migrate to and accumulate either near the air/film or near the substrate/film interfaces and can have adverse effects on film water sensitivity, gloss retention, reduced adhesion on substrate, film haze, and on film hardness. Some of these effects can be mitigated by using reactive emulsifiers. For example, WO 92/09667 A describes the use of fatty acid alkoxylates of the general formula: R—CO—NH—(CmH2m)—O-(AO)n—H, where R is C7 to C23 polyunsaturated alkyl, m is 2-4, AO is an alkylene oxide residue, and n is 2-30, which are described as participating in the curing of the binder, thus reducing some of the adverse effects of surfactants. However, there is still a need to further improve film properties.
The present invention is based on our finding that certain types of ethylenically unsaturated surfactants are effective emulsifiers for resins, preferably alkyd resins, and particularly unsaturated curable alkyd resins. The use of the surfactants can result in well cured films without deactivating typical alkyd drying catalysts, giving films of high hardness and good water resistance, whilst maintaining good gloss.